30mm Machine

20mm Ammo Dimensions

Mk 22 Engineering Prototype

Test Results

The 20mm Mk 22 Mod 0 was first tested in November 1%7 at NOSL firing Mk 100 series ammunition. A 30mm version firing XM639 ammunition was fired in February 1968. These tests demonstrated the basic soundness of the weapon design. However, size restrictions made the weapon marginal for the Mk 100 ammunition.

Using 20mm M50 series ammunition three newly built Mk 22 guns had fired over 13,000 rounds at Louisville by May 1969. Two of the guns were then tested at NWLD and out of 2100 rounds fired there were 130 malfunctions for a mean round between stoppages of 16. The immediate cause was determined to be that a hard mount was used by NWLD while a soft mount had been used at NOSL. It was determined at Louisville that, using a rigid mount, the receiver would sometimes flex to the point where the bolt would not unlock.

A redesign of the receiver and feeder followed and further testing showed that while the flexing of the receiver had been eliminated there were still difficulties with the feeder. A new feeder was designed and by May 1971, a total of 13,500 M50 series rounds had been fired. In that month the feeder was further improved so that the feeder lever operated directly off the barrel extension. A total of 28,530 rounds, including some electric primed ammunition, had been fired by the first week in August 1971.

A second series of tests began at NWLD in mid-August 1971. These tests were part of a "shoot off' between the Mk 22, the Mauser Model B, the GE 120B, and the AME 621.

In those tests, the Mk 22 fired a total of 14,500 rounds with twenty-three malfunctions which involved only eight gun components. All environmental tests were passed and problems which occurred during the tests were corrcctcd.

As a result of the Dalilgrcn tests eleven design changes were made to correct the design deficiencies which accountcd for all of the malfunctions.

The two test guns were modified in accordance with the design changes and were returned to NWLD in April 1972 for further test firing and safety certification.

The report on that test states that approximately 4500 rounds were fired in each of the two Mk 22 Machine Guns and no gun and ammunition compatibility problems were encountered. Measurements taken during firing indicated satisfactory ammunition performance.

A comparison of the firing records obtained for

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